The present invention relates to an electronic circuit
for controlling circuit components connected electrically in series or in a matrix-like network which is part of a shift register.
Controlling such serially connected or matrix connected circuit components is necessary for addressing the row and column conductors of a liquid crystal display screen. Such active-matrix liquid crystal-display screens (so-called AM-LCDs) are to be used increasingly in the future to replace display devices with cathode ray tubes in television and data processing, since they have a number of advantages: reduced weight, flat structure, no distortion of the picture produced, low control voltages, reduced power consumption, possible use as a light valve in a projector, high resolution, no generated X-radiation as in the case of a cathode ray tube, no strong magnetic and electric fields originating from the display device and economical manufacture, which is particularly suitable for large screen applications.
Liquid crystal-display screens have a matrix-like arrangement of image spots. Each image spot is associated with a circuit component. The circuit components are multiple thin film transistors. The image information is fed to the columns and is written line-wise into the image spot memory by the circuit components. Thus the lines or rows must be controlled so that only one line conductor of the N lines of the display screen has a sufficiently high potential for 1/N-th of the image display time, so that the image spot capacitance can be changed to the data voltage corresponding to the image information by the circuit component. It must be guaranteed that the image spot capacitance cannot be discharged by the circuit component during the remaining image repetition time.
In many applications, e.g. in display screens with a comparatively large number of image spots and/or smaller image size it is advantageous to integrate the circuit arrangement for controlling the line or row conductors in the display screen substrate. This requires that the circuit arrangement be manufactured in the same technology as the display screen matrix.
Few methods of integration of shift registers for matrix addressing directly in the glass substrate in a technology compatible with the manufacturing method of the display screen device are described in the literature (Y. Oana et al.: 1984 SID Symposium Digest pp. 312-315; S. Morozumi et al.: 1984 SID Symposium Digest pp. 316-319; J. Ohwada et al.: Conf. Record of the 1988 Inter. Res. Conf. pp. 215-219; B. W. Faughnan et al.: Proc. of the SID Vol. 29/4 1988 pp. 279-282; I. De Rycke et al.: Conf. Record of the 1988 Inter. Res. Conf. pp. 70-73; M. Akiyama et al.: Japan Display 1986, pp. 212-215; K. Khakzar et al.: Japan Display 1989 pp. 438-441; Y. Nishihara et al.: 1992 SID symposium Digest pp. 609-612; Dae M. Kim et al.: 1990 SID Symposium Digest pp. 304-306). These driver circuits comprise an N-stage shift register and N-output driver stages, in which N is the number of lines of the liquid crystal-display screen. The output stages must be in a position to rapidly charge and discharge the capacitive load to be driven, which is composed of the input capacitance of the circuit components and the cross-over capacitance of the line and column conductors.
From the literature both static shift registers (Y. Oana et al.: 1984 SID Symposium Digest pp. 312-315; S. Morozumi et al.: 1984 SID Symposium Digest pp. 316-319,; B. W. Faughnan et al.: Proc. of the SID Vol. 29/4 1988 pp. 279-282; M. Akiyama et al.: Japan Display 1986 pp. 212-215, Y. Nishihara 1992 SID Symposium Digest pp. 609-612) and also dynamic shift register (S. Morozumi et al.: 1984 SID Symposium Digest pp. 316-319; J. Ohwada et al.: Conf. Record of the 1988 Inter. Res. Conf., pp. 215-219; I. DeRycke et al.: Conf. Record of the d1988 Inter. Res. Conf. pp. 70-73; K. Khakzar et al.: Japan Display 1989 pp. 438-441) are known for addressing the line and column conductors of a display screen. One stage of a static shift register generally comprises two bistable sweep circuits which include at least 12 transistors, e.g. in thin layer technology. Dynamic shift register stages comprise two serially connected inverters and need only four to six transistors (4 transistors for example in the device described in K. Khakzar, Japan Display 1989, pp. 438-441). Similarly several different devices are known for the additionally required output driver stages. One simple device as described in Y. Oana et al.: 1984 SID Symposium Digest pp. 312 to 315 comprises two serially connected inverters. Also the so-called push-pull stages, which have two broad-band thin film transistors, are used as an output driver stage. Several inverter stages (see J. Ohwada et al. :Conf. Record of the 1988 Inter. Res. Conf. pp. 215-2319; B. W. Faughn et al.: Proc. of the SID Vol. 29/4 1988 pp. 279-282; M. Akiyama et al.: Japan Display 1986 pp. 212-215) or amplifier circuits (see J. Ohwada et al.: Conf. Record of the 1988 Inter. Res. Conf. pp. 70-73) are included in the shift registers and push-pull stages. Only at times one transistor of the push-pull stage is conducting and connects the output either with a high or a low potential.
In the case of line control the total number of required transistors per line control stage increases to about 4 to 12 because of the necessary additional output stages. Also very extensive control circuits are required because display screens with greater resolution or definition have a correspondingly larger number of lines and columns (about 500 to 2000). The same problem results naturally for serially connected arrangements of circuit components, for example the circuit components for reading out the signals of an image scanner sensor line or circuit components for control of switching transistors of a press device.